Objective To investigate the immunologic enhancement of Porphyra polysaccharide. Methods Porphyra polysaccharide in different dosages (0.025,0.050,0.150g?kg~(-1)) were injected intraperitoneally into the immunosuppressive mice induced by cyclophosphamide for 7d. On day 8,the cytotoxic activity of NK cells,the levels of interferon-?(IFN-?)and nitric oxide (NO)in the cultured supernatants of spleen cells were determided. Results The cytotoxic activity of NK cell,the levels of IFN-? and NO produced by cultured spleen cells from the group of mice treated with 0.150g?kg~(-1) of Porphyra polysaccharide were higher than those from model group. Conclusion Porphyra polysaccharide could enhance immunological functions to a certain degree in immunosuppressive mice.